Roland 100M 130 VCA - Verified - PCBs now available

[frequencycentral]

Another one in my series of 100M cloned circuits, the 130 VCA, adapted for the CA3080 (BA662B being rare and rocking horse shit - at least CA3080 are get-able). Not yet verified - could do with a second set of eyes if anyone would like to check it.

What's included:

- 2 x Audio inputs plus pads for an additonal one
- Initial Gain pot
- 2 x CV inputs plus pads for an additonal one
- Provision for Lin/Exp switch
- option to short out input/output caps for DC processing
- I used 2 x 22uF polarised caps back to back in place of 1 x 10uF NP
- Additional pads for various trimmer sizes

What's not included:

- I didn't include the LEDs for signal/overdrive. Roland used an additional 22v feed to power the LED sub-circuit. I don't think many of us will have that in our systems. Besides, IMO, it's a big bit of circuit just for 2 blinkenlights. However, I've added a (blue) pad should anyone wish to implement this themselves.





I'm not going to have time to verify this layout for a few weeks, but I have built this VCA before using the components specified. I've got a few vintage metal can CA3080 myself, but I'm also currently in negotiation with a friend who has a bulk lot of genuine CA3080, so I may be able to offer a mini kit of PCB + CA3080 if the deal comes off.

[frequencycentral]

Ok, this PCB is now verified. Woot!



The exponential is particularly snappy! Just out of interest, I used BC547, BC557 and 2N5485 - perfect. I'm just gonna move a few components on the layout that are a little too close to the header. PCBs are available at £10 GBP per board, shipped anywhere. Provision for Doepfer and MOTM headers onboard Delivery will not be quite so quick on these, as I'm midway through etching the VCLFO PCBs. If you're interest, Paypal gift to:

rickholt22 (AT) hotmail (DOT) com

Please state your forum name, full address etc.

[defog]

Kick ass. Well, I know what VCA I'm building now for my synth project. Thanks Freq!

[defog]

Hey Freqencycentral,

I had problems getting the VCA to work. I'm thinking because I'm using a BFA245a for Q1 according to the schematic that if the flat side of the FET is facing away from the pots, the Source should be going to R12 (10K) top, and the Gate is going to C2 (47p) bottom, and the Drain is going to the postitive rail middle that I need to swap the legs on the BFA245 around. Does that sound right? The datasheets I've read show with the rounded side facing towards you that it reads D-S-G, and putting a BFA245a into place as show in the layout would make it Gate on bottom, source middle, and drain top. Please correct me if I'm wrong. Should Drain go to +rail, Gate go to the 47p to ground, and source to the 10k (R12) to the - rail? Thanks.

[defog]

Just replaced the BF245b with a 2N5485 in the same position as your layout. Will try it out tomorrow and see what happens. I think I have my switching wired screwy though for Exp/Lin and the AC/DC pot. Not quite sure how to approach that, so any help would be wonderful Thanks.

[defog]

I currently have the Exp/Lin common wired to a SPDT with one side going to exp, the middle common, and the linear on the top.

The coupling DPDT I have the top and common on the left two points on the PCB wired to the top and common, and the opposite poles on the right wired to the Common and bottom of the switch.

I have a wire coming out of the low output to test. Q2&4 are BFC-550s, Q3&Q5 are 2n5087s matched as close as possible with hfe. And like I said above, 2n5485 is the FET replacing BF245b. I've done continuity testing and everything checks out right. The resistor series show are not touching (even though it looks that way in the pics).

[frequencycentral]

Here's the wiring for the AC/DC DPDT:



Re the FETs, source and drain are interchangable, so as long as the FET you use is a DSG or GSD pinout you should be fine as long as the gate gets the input from the CA3080 pin 6. I have used both BF245 and 2N5485 in this circuit with success.

[defog]